1. Electromagnetic (EM) Spectrum

2. The Electromagnetic Spectrum
Light, a type of radiation, is part of the electromagnetic spectrum.
The electromagnetic spectrum is made up of different types of radiation.
The different types of radiation have different properties and behaviour.
All electromagnetic waves can travel through space.
All electromagnetic waves travel at the same speed [300,000,000 m/s in a vacuum].
TRUE/FALSE

3. Dispersion of white light

4. Colour, wavelength and amplitude
We can see the relationship between colour, wavelength and amplitude using this animation F

5. Electromagnetic Spectrum
Although all EM waves travel at the same speed, their wavelength [] and frequency [ƒ] can be different.
Waves that cook food.
Waves that cause sun-tans.
The properties, dangers and uses of EM waves depends on the wavelength [].

6. EM waves are transverse waves

7. Electrical/Magnetic field
TRANSVERSE WAVES
The electric and magnetic fields vibrate at right angles to the direction of movement of the energy
Electrical/Magnetic field
Energy Movement

8. Wavelength () increases
Radio
Micro
Infra-Red
Light
Ultra-Violet
X rays
Gamma
Electromagnetic Spectrum
Wavelength () increases
Gate X Usually Lets In Most Radiation
Can you think of a phrase that would help you remember this order?
Low frequency
Long wavelength
Low energy
Least penetrating
High frequency
Short wavelength
High energy
Most penetrating
High frequency
Short wavelength
High energy
Most penetrating
Low frequency
Long wavelength
Low energy
Least penetrating

9. Uses and dangers of EM radiation
Need to know the uses and dangers of the various radiations:
Radiation
Uses
Dangers
Gamma
X-rays
Ultraviolet
Light
Infra red
Microwaves
Radio waves

10. EM Radiation: Uses: Dangers:
Gamma
Kills harmful bacteria in food, sterilising surgical equipment, killing cancer cells, gamma camera.
High doses can kill cells, lower doses can cause cells to become cancerous.

11. EM Radiation: Uses: Dangers:
X rays
How do hospital workers limit their exposure to Gamma and X rays?
Hospital workers limit exposure to Gamma and X rays by standing behind lead shields or by leaving the room when the radiations are being used.
Shadow pictures of luggage and inside the human body.
High doses can kill cells, lower doses can cause cells to become cancerous.

12. X rays
How are X rays slides formed?
X rays can penetrate soft tissue but not b_____. X rays are a_______ more by some materials than others. P________ f____ is used to detect X rays.
one
bsorbed
hotographic
ilm
What colour does the photographic film go
when it is hit by X-rays?
black

13. EM Radiation: Uses: Dangers:
Ultraviolet
Sun beds, fluorescent lamps and security marking.
The higher the frequency of the radiation, the more dangerous it is. So gamma is more dangerous than X rays or ultraviolet.
Which type of radiation is the most dangerous?
High doses can kill cells, lower doses can cause cells to become cancerous.

14. EM Radiation: Uses: Dangers:
Light
Seeing and endoscopes.
Blindness

15. EM Radiation: Uses: Dangers:
Infrared
Remote controls (TV/VCR), radiant heaters, grills, optical fibre communication, night vision.
Skin burns

16. Night vision
Light is hot.
All objects above absolute zero emit infrared radiation. The hotter an object is, the more heat radiation it emits. Some animals and cameras can detect infrared radiation and are able to build up a heat picture.
Which are the hottest/coolest parts of the image shown?
Dark is cold.

17. EM Radiation: Uses: Dangers:
Microwaves
Satellite communication, mobile phone networks, cooking.
Internal tissue heating.

18. Microwaves How do microwaves cook foods?
Microwaves can be used in c_____ because many foods contain w____ molecules. Microwaves of the right w________ are able to make the water molecules v_______. This causes the food to get h____.
ooking
ater
avelength
ibrate
otter

19. EM Radiation: Uses: Dangers:
Radio waves
Communication and astronomy

20. Radio waves
The longer wavelength radio waves from a transmitter reflect off the Earth’s outer atmosphere (ionosphere).
How do radio signals from the UK reach around the globe?

21. Getting hotter
If electromagnetic radiation is incident upon a material what effects could it have?
An alternating current could be induced in the material, with the same frequency as the incident radiation.
The temperature of the material could increase.
70º C
50º C
30º C
21º C

22. EM Questions
1) Match up the following parts of the electromagnetic spectrum with their uses :
Gamma rays Allow us to see
Radio waves Remote Controls
Ultra Violet ‘See’ broken bones
Visible Carry TV signals
Microwaves Satellites
X rays Sterilise equipment
Infra Red Causes sun-tans

23. EM Questions 2) Which radiations are missing from below? ___________
Gamma A
Ultraviolet
Light
Infrared B
Radio waves
___________
X rays
Microwaves

24. The wave equation c = 300,000,000 m/s Speed of light/c (m/s)
Frequency/f
(Hz)
wavelength/
(m)

25. Wave equation questions
Q1) what is the frequency of microwaves with a wavelength of 20cm?
Frequency = speed/wavelength
= 300,000,000/0.2
= 1500,000,000 hertz
Q2) What is the wavelength of radio waves with a frequency of 16MHz?
Wavelength = speed/frequency
= 300,000,000/16,000,000
=18.8m

26. Total Internal Reflection
Optical fibres, that are used in communication, use total internal reflection.
What are the applications of total internal reflection?
You could be asked to draw on the path of the beam in an exam.
A beam of light enters the optical fibre….
…NOTE how it is refracted as it enters the fibre…
…it travels down the fibre through repeated total internal reflections.

27. Digital and analogue
What is the difference between a digital signal and an analogue signal?
What could they look like graphically?
Digital signals can only be in one of two states, e.g. 0 or 1.
Analogue signals are a continuously changing variable.

28. Digital compared to Analogue
ADVANTAGES
 Signals are clearer because noise (interference) can be removed
 Carry much more information.
Digital hardware is much smaller.
Easier to send digital over long distances because signal doesn’t weaken as fast.
DISADVANTAGES
 Digital hardware is expensive at the moment.
 Although digital signals are unaffected by electrical interference, they don’t give a complete signal [just lots of samples] - some people feel that analogue vinyl records sound better than digital CDs for this reason.
Electrical storms and random thermal noise.
Noise is any unwanted information.
Which signal is most prone to noise?
Which signal carries the most information?
Analogue
Examples of noise are?
What is noise?
Digital